1. Technical Field
The invention relates to the field of thermoelectric cooling devices, and more particularly, to solid-state cooling devices that include Peltier junctions to aid in the cooling process.
2. Description of the Related Art
Temperature is a crucial parameter in an enormous number of physical, chemical and biochemical processes and particularly in a variety of medical and electronic devices that can be operated more effectively at very cold temperatures. While thermoelectric coolers currently in use can readily reach and maintain temperatures in a range of 300 K (room temperature) to 230 K, there is no solid-state cooler capable of reaching temperatures below 160 K.
Thermoelectric coolers, also known as Peltier coolers, have existed for many decades, but they have been unable to achieve temperatures cooler than about 210 K primarily because their efficiency drops in proportion to the temperature difference across them. This fact is partly due to the temperature dependence of the properties of thermoelectric materials, but is also largely due to the traditional xe2x80x9cbrute forcexe2x80x9d structure of refrigeration devices including Peltier coolers
FIG. 1 illustrates a standard Peltier cooler designed to reach low temperatures (xcx9c200 K). It consists of a cascade of zigzag structures of junctions between n-type and p-type semiconductors, sandwiched between ceramic plates. When a current flows through the structure, its top face absorbs heat from the environment and its bottom face releases heat to the environment. In other words, the device pumps heat from one face to the other.
Several conflicting processes are at work in this type of Peltier cooler. The current flow pumps heat as a result of the Peltier effect, but heat is generated by the I2R resistive heating. As heat is pumped, a temperature difference builds between the two faces of the device, so the Seebeck effect generates a voltage which opposes the current creating the temperature difference. Ordinary thermal conduction also allows some heat to flow back toward the cold side. The Thompson effects nearly cancel out in this device, so the Thompson effect is usually ignored.
The maximum temperature difference which can be developed by a standard single-stage Peltier cooler with no heat load is about 70 degrees Centigrade. Larger temperature differences, up to 140 degrees Centigrade, can be attained in multistage devices like that illustrated in FIG. 2. However, the pumping efficiency becomes very poor because each stage not only pumps heat that must be pumped in turn by the next stage, but each stage also generates resistive heat that must be pumped in turn by the next stage.
From a different art, in the design of ordinary fluid heat exchangers used in the heating industry it is standard practice to run fluid in opposite directions through two pipes in thermal contact as illustrated in FIG. 3. This works much better than moving the fluid in the same direction through the two pipes. A significant feature of fluid counterflow heat exchangers is that the temperature difference between the two pipes is nearly zero everywhere along the exchanger, even though there can be a very strong temperature gradient along the length of the pipes.
Fluid counterflow also occurs in the natural world where a continuous loop may form a fluid counterflow exchange amplifier, which is essentially a counterflow exchanger in which the fluid flows as illustrated in FIG. 3, but in which a component of the fluid is separated from the incoming flow and pumped across to the outgoing flow as indicated in FIG. 4. This occurs, for example, in the ocean, where nutrients are concentrated at the shoreline by a counterflow process. The incoming fluid flows toward the shore along the bottom carrying nutrients, is warmed and flows away from the shore along the surface while gravity pulls the nutrients down to the incoming flow from the outgoing flow, trapping the nutrients in a loop. In another example, one mechanism by which living organisms maintain large ion concentration gradients in certain tissues such as the kidney, is by counterflow amplification of the solute concentration in fluids flowing across semi-permeable membranes that connect kidney nephrons to blood vessels in counter-directional flow.
There is a need in the art to provide a thermoelectric cooler of a new design which can overcome the limitations of previous coolers and avoid some of the constraints that material properties impose on thermoelectric cooling. Further, there is a need to provide miniature thin film solid state coolers that are useful in computer applications.
The present disclosure fulfills these needs and others that will become apparent from the present description, by providing a thermoelectric cooler design that combines the advantages of counter-current flow with the advantages of Peltier cooler and which can be fabricated in a miniature scale using thin-film solid state materials used in the semiconductor arts.
More particularly, one aspect, the thermoelectric cooler provided herein includes, a counter-current exchange conductor having a conductive path between a first conductive zone and a second conductive zone, where current flows in substantially an opposite direction in the first conductive zone with respect to the second conductive zone; and a Peltier junction in thermoelectric contact between the first conductive zone and the second conductive zone.
Certain embodiments of this aspect include a plurality of Peltier junctions in thermoelectric contact between the first conductive zone and the second conductive zone. In other embodiments, the Peltier junction includes a heat transfer material, a first conductive material in thermoelectric contact with the heat transfer material and in conductive contact with a second conductive material different than the first conductive material, and a third conductive material different from the second conductive material, the third material in thermoelectric contact with the heat transfer material and in conductive contact with the first material.
In more particular embodiments of this aspect, the heat transfer material includes a warming region and a cooling region, the warming region being in thermoelectric contact with a first zone of the counter-current exchange conductor and the cooling region being in thermoelectric contact with the second zone of the counter-current exchange conductor. Other particular embodiments of this aspect include the use of a plurality of Peltier junctions that include the aforementioned heat transfer material.
In certain embodiments, the thermoelectric cooling apparatus includes thin film conductive materials. In particular embodiments, the second or third conductive material described above includes (Bi,Sb)2(Te,Se)3.
In another aspect, the invention provides a thermoelectric cooling apparatus having a cold end and a hot end, wherein the hot end is about room temperature and the cold end is about 70-100 degrees K.
In yet another aspect, there is provided, devices that include various types of thermoelectric cooling apparatus having the aforementioned features. One particular embodiment of this aspect is a superconductive quantum interference device.
In still another aspect, there is provided a method of cooling an object, that includes the steps of: forming a counter-current exchange conductor to have a conductive path between a first conductive zone and a second conductive zone; so that current passing through the counter-current exchange device flows in substantially an opposite direction in the first conductive zone with respect to the second conductive zone; forming a Peltier junction in thermoelectric contact between the first conductive zone and the second conductive zone; passing current through the counter-current exchange conductor through a circuit that includes the Peltier junction to form a cold end; and cooling the object by placing it in radiant, thermoconductive, or conductive contact with the cold end.
In another aspect, the thermoelectric cooler provided herein can be run in reverse, which provides a method of generating electricity from a temperature gradient that includes the steps of: forming a counter-current exchange conductor to have a conductive path between a first conductive zone and a second conductive zone; so that current passing through the counter-current exchange device flows in substantially an opposite direction in the first conductive zone with respect to the second conductive zone; forming a Peltier junction in thermoelectric contact between the first conductive zone and the second conductive zone; positioning a first portion of the current exchange conductor in proximity to a substance having first temperature and positioning a second portion of the current exchange conductor in proximity to a substance having a second temperature; and drawing electricity from the first or second conductive zones.
As will be apparent to one of ordinary skill in the art from the disclosure provided herein, counter-current thermoelectric cooler devices can be embodied in numerous forms for application to a wide range of fields. The ability to cool small volumes to below 100 K allows practical application of high-temperature superconducting quantum interference devices (SQUID""s) in NMR imaging and infrared imaging. In addition, the present cooler is useful in computer applications wherever it is possible to maintain a superconductive integrated circuit at 100 K on a printed circuit board, for example, in the internal environment of a desktop computer. Devices cooled by the thermoelectric cooler provided herein make a wealth of new applications possible, taking advantage of the high switching speed, high density and low power consumption of superconducting electronics as well as the high sensitivity of superconductive IR arrays and magnetic field sensors. In other embodiments, the cooler will enable researchers to maintain precisely controlled temperature gradients of very high magnitude in small regions, to study and control biochemical processes and to measure thermal and electronic properties of materials. In still other embodiments, the cooler is useful in spectral hole-burning optical memories that provide thousand times more capacity than current media. In yet other embodiments, the cooler is useful in sensitive coupled quantum well devices and in molecular electronics.